NOTE: A growing number of researchers now
either
divide the Monera into two distinct kingdoms: Eubacteria
(the true bacteria) and Archaebacteria(bacteria-like organisms that live in extremely harsh anaerobic
environments such as hot springs, deep ocean volcanic vents, sewage
treatment plants, and swamp sediments) or define 3
domains of living things: Archaeo (archaeobacteria), Bacteria (all other
bacteria, blue-green algae, and spirochetes), and Eukarya (organisms with
distinct nuclei in their cells--protozoans, fungi, plants, and animals).
Domains are a level of classification above kingdoms. Viruses, prions, and other
non-cellular organic entities are not included in the
domains and kingdoms
of living things.

The numbers of named and estimated total species
were derived from Gibbs, W. Wayt (2001) "On the Termination of
Species", Scientific American Vol. 285, No. 5.